This invention relates to an electrode seal for an electric furnace having one or more large diameter electrodes extending through an opening in the furnace roof.
Electric arc furnaces used for melting metals usually comprise a crucible and one or more generally vertical carbon electrodes supported so as to depend into the crucible. In order to contain fumes, maintain a desired atmosphere within the furnace and control heat loss and noise, it is common practice to provide such furnaces with a lid or roof having apertures through which the electrodes depend.
Particularly during the initial stages of melting a charge, current surges through the electrode apply very substantial electromagnetic forces, which can cause significant lateral deflection of the electrodes. Therefore, it is necessary to provide a clearance between the electrode and the aperture in the furnace roof in order to prevent the furnace roof from being damaged by movement of the electrode. However, as such arc furnaces operate at close to atmospheric pressure, and can go into positive pressure, harmful gases such as oxides of nitrogen and carbon-monoxide, are released into the atmosphere through the gap, therefore making it desirable to provide some sort of seal arrangement between the electrode and the furnace roof.
The seal must prevent substantial escape of fumes through the gap while permitting vertical and lateral movement of the electrode. The provision of adequate sealing is especially difficult in electric arc furnaces where it is necessary to completely withdraw the electrode from the furnace. Examples of this type of furnace include arc furnaces used to melt scrap steel. Such furnaces have a single electrode which is completely withdrawn from the furnace several times per hour to allow fresh scrap steel to be charged through the hole in the furnace roof. After the scrap material is charged, the electrode is again inserted through the aperture in the furnace roof and bores through the solid scrap material until it reaches a desired depth. During this boring operation, significant noise is generated by arcing between the electrode and the solid scrap material. The noise typically abates as the material is melted.
Although the prior art contains numerous examples of electrode seals to solve this very problem, none has proved generally acceptable to operators of arc furnaces used for the melting of steel, and particularly where complete withdrawal of the electrode is required. Therefore, many electric arc furnaces continue to be operated without any seal at all.
The present invention overcomes at least some of the problems of the prior art by providing an electrode seal for electric arc furnaces which is effective to substantially reduce fumes and noise associated with melting of metals in arc furnaces, is of relatively simple and economical construction, can be made sufficiently light to be safely supported on the refractory portion of the furnace roof surrounding the electrodes, is compatible with repeated complete withdrawal of the electrodes from the furnace, and can help extend the life of the electrode and the refractory roof.
The electrode seal according to the invention comprises an annular support ring having an internal diameter substantially greater than the diameter of the electrode, and which is secured to the furnace roof by a plurality of mounting feet. The annular support ring has an upper annular sealing surface on which is received an annular sealing ring having an internal diameter which is approximately the same as the diameter of the electrode to form a substantial seal therewith. The sealing ring has a lower annular sealing surface which engages the upper sealing surface of the support ring, while allowing limited sliding movement of the sealing ring along its lower annular sealing surface.
Thus, the present invention provides an electrode seal of simple construction in which escape of gas through the aperture in the furnace roof is greatly reduced by a tight-fitting sealing ring, which is laterally movable to account for lateral movement and misalignment of the electrodes.
Testing of the electrode seal of the present invention has shown that the electrode seal effectively inhibits escape of gases from the furnace, and also significantly reduces the noise level in the vicinity of the furnace.